Minigrids offer a viable solution for extending electricity access to underserved areas beyond the reach of main-grids. Their sustainability is crucial for rural electrification prospects in Sub-Saharan Africa. Using Ostrom's IAD framework, we conduct a socio-cultural and institutional analysis of minigrids across their development stages. We map sector actors and their respective roles in the minigrid sector providing a framework for their interactions and choices towards sustainable outcomes. We further present a comparative institutional assessment of Uganda and Tanzania's minigrid sectors; analyzing outcomes and constructing a diagnostic framework of the causal actor interactions and exogenous contexts hindering sector sustainability. Our study reveals the inherent challenge posed by the complex interdependencies within the minigrid sector and its relationship with adjacent sectors. It further uncovers significant institutional inefficiencies in the minigrid sectors of Uganda and Tanzania. We advocate a flexible solution strategy, wherein, regulators strategically modify the adaptable components of the IAD framework considering the specific root causes of problems. This approach allows for targeted interventions through precise adjustments to effectively address underlying issues. Additionally, we emphasize the importance of policy integration mechanisms with adjacent sectors and a policy design process that incorporates the core values of sector actors.